1. Field of the Invention
This invention relates to radial ply tires designed to be mounted on motorcycles.
2. Discussion of the Related Art
The functioning of tires mounted on motorcycles, and more generally on any vehicles with two wheels placed one in front of the other (mopeds, motorcycles), is entirely different from that of tires mounted on automobiles, trucks, trailers, etc. For example, the tires of the first category are subject to a very wide range of so-called camber angles while those of the second category are used only in configurations where the camber angle is almost zero, or at least very small.
To keep a vehicle on its path, the tires must develop cross thrusts. In tires of the first category, these thrusts are mainly so-called camber thrusts (because they are induced by a camber angle) whereas in tires of the second category, these thrusts are mainly so-called slip thrusts (because they are induced by the slip angle that the tire tread makes in relation to the vehicle path).
When it was desired to design radial ply tires for motorcycles, not all of the advantages pertaining to this design, encountered in its other applications, were found to exist. This appears to be due to the fact that the thrusts of a radial ply tire develop in a way totally different from what happens for a so-called bias tire. In particular, the part of the tire thrust due to camber thrusts in a radial ply tire is very small. A degraded behavior results, i.e., a deteriorated ability of the motorcycle to follow the path imposed by the driver. Moreover, instabilities in straight line travel are frequently observed: the motorcycle oscillates around the desired rectilinear path.
Attempts have already been made to remedy this problem by providing coordinated tire structures for the front and rear tires. U.S. Pat. No. 4,510,983 provides a relation for linking the angles of the tread reinforcement threads for the front tire and the rear tire. This proposal, however, proved unable to impart a good handling behavior, regardless of the use and/or the other components of the tires.